Ask them the same question is various ways multiple times, preferably several minutes or conversations apart. For example:

• Are you doing anything later?
• What are you doing later?
• Got any plans for after this?
• Are you free later?

Once they catch on or start getting frustrated, suggest activities that conflict with their plans but would be rude to argue because you’re being caring or excited to partake:

• Maybe you could get some rest tonight.
• Want to go on a drive with me to the beach?
• There’s a video I saw on YouTube that is so pertinent to [something central to their current life]. I want to show it to you. proceed to pull up a 2+ hr documentary
• Oh, my favorite restaurant is having a deal, I haven’t been in soooo long and starving. Let’s go for dinner!
• I have a surprise for you later that I knowwww you’ll love. I’m so excited.

Note: This may damage your relationship with them or cause them to think you are mentally/emotionally unwell.

A separate idea is, when interacting with someone you meet occasionally, where the exact same outfit every time, but only wear that outfit around them. This would be even better if you share the same social circle because eventually they will bring it up to others that will disagree with them.